The present invention concerns a method of manufacture of tires and an assembly drum making it possible to use the method.
The invention concerns, in particular, the manufacture of a tire comprising a carcass reinforcement, at least one reinforcing bead wire in each of the beads of the tire, around which the carcass reinforcement is wound, forming a turn-up, said tire being such that, in contrast to what is generally done, the turn-up of the carcass reinforcement is arranged between the bead wire and the carcass reinforcement itself. One can refer, in particular, to publication FR 2.716.645 for a best comprehension of the tire.
It is known that, in order to make turn-ups of the carcass reinforcement around the bead wire, the assembly drums are equipped with carcass reinforcement turn-up devices. It is possible to cite, by way of example, U.S. Pat. No. 3,698,987, which describes a turn-up device comprising a first inflatable bladder that is generally toroidal and whose displacement necessary for the turn-up operation is carried out by an intermediate element consisting of a second inflatable bladder or metal collar which exerts a transverse thrust on the first bladder. In U.S. Pat. No. 4,087,306, the turn-up device consists of a turn-up bladder which develops by itself, under the sole effect of elevation of inflation pressure, the rolling movement in the transverse direction necessary for carrying out the turn-up of the carcass reinforcement.
These drums and turn-up devices make possible the manufacture of tires using a process stage consisting, once the carcass reinforcement is positioned on the uninflated drum, that is to say in its smaller circumferential diameter, and the bead wires are axially opposite their locking position relative to the carcass, of inflating the drum in order to fix the positioning of the bead wires on the carcass reinforcement, and then of actuating the turn-up device, making possible the turn-up of each lateral end of the carcass reinforcement around the corresponding bead wire.
Such drums do not lend to a modification in the method of manufacture aimed at situating the turn-up of the carcass reinforcement under the bead wire. Insofar as operation of the turn-up device is made subject to the presence of a fixed point, consisting of the bead wire, around which the turn-up of the carcass reinforcement is made, it is impossible to see how the carcass reinforcement could be turned up, using the bead wire to fix the place of bending, while stringing the turn-up radially under said bead wire.
The invention therefore concerns a method of manufacture of a tire, in which the turn-up of the carcass reinforcement is positioned between the bead wire and said reinforcement, and an assembly drum making it possible to use that method.
According to the invention, the method of manufacture of a tire includes the following steps:
depositing a carcass reinforcement on a generally cylindrical receiving surface,
then depositing a strip of rubber compound on one of the ends of the carcass reinforcement,
then turning up said end around the strip of rubber compound,
and positioning a bead wire on the turn-up thus made.
The turn-up of the end of the carcass reinforcement around the strip of rubber compound is advantageously made by radially raising said end, bringing the bead wire axially toward the center of the carcass reinforcement up to the bearing of the end on the bead wire, and continuing the axial advance of the bead wire in synchronization with expansion of the receiving surface.
In particular, the end of the carcass reinforcement is raised radially by pressing radially toward the outside of the drum, just under the strip of rubber compound. A turn-up of the carcass reinforcement is thus made around the strip by tilting the latter.
The invention also concerns a tire assembly drum having a body with a receiving surface for the products to be assembled, said element being mounted on a center shaft, characterized in that it contains at least one lifting device situated at one of the ends of the receiving surface, which comprises a plurality of lifting fingers distributed circularly around the center shaft, said fingers extending appreciably radially and presenting a bearing surface for the products to be assembled, said fingers being deployable essentially radially toward the outside of the drum movement of translation under the action of control means.
xe2x80x9cEssentially radiallyxe2x80x9d means a possible axial movement of the lifting fingers, if it exists, is negligible in the desired action.
Such a lifting device containing radially deployable elements makes it possible to elevate, relative to the receiving surface, the end of the products to be assembled and, owing to the composition of the elements in the form of fingers extending appreciably radially, to leave said raised end free and therefore accessible.